A. Field of the Invention
The present invention relates to suspension fork rotatably supported on a head portion of a bicycle frame, and to a bicycle on which the suspension fork is mounted.
B. Description of the Related Art
It is well known in the art to equip bicycles with a suspension fork instead of a rigid fork, for the purpose of absorbing shock generated during riding. Suspension forks for the front wheel of a bicycle are generally categorized as fork type, in which two suspension mechanisms replace parts of the fork legs, and head mounted type, in which a suspension is disposed between the handle post and the fork stem.
The suspension fork for the fork type is similar to one used in a motorcycle. However, since this involves two separate suspension mechanisms, the number of parts is increased, and there is an increase in weight and cost.
With respect to a head mounted suspension fork, it is possible to reduce the number of the parts as well as to reduce the weight and cost, since there is only one single suspension mechanism. The HEADSHOCK.RTM. (a product of Cannondale Corp.) is known as one type of head mounted suspension fork.
This type of suspension fork is provided with a fork portion for supporting a front wheel, a first fork stem integrally formed with a handle post and rotatably supported on a head portion, a second fork stem whose tip end is disposed in an interior of the first fork stem, a spring member for urging the two fork stems in a direction away from each other, and a coupling means composed of a needle bearing for securely coupling the first and second fork stems to be relatively movable in an axial direction but unrotatable relative to each other. Typically, the spring member is urethane rubber or a hydraulic cylinder. The needle bearing is interposed between an inner circumferential surface of a lower portion of the first fork stem and an outer circumferential surface of an upper portion of the second fork stem.
With this type of suspension fork, when a shock is applied to the front wheel, the second fork stem is guided by the needle bearing within the first fork stem and is moved upward against the spring force of the spring member to thereby absorb the shock. In addition, when the handle is manipulated, the first fork stem is rotated together with the handle and the second fork stem is rotated through the needle bearing. As a result, the front wheel is steered in a desired direction.
However, the coupling means is composed of a needle bearing, which is expensive. Accordingly, such a suspension fork is mounted only on an expensive mountain bike. In addition, the needle bearing is interposed between the first fork stem and the second fork stem, thus the outside diameter of the first fork stem must be larger than the standard diameter (25.4 mm) of the fork stem on regular rigid forked bicycles. This prevents this type of suspension from being used on a wide variety of bicycles.